ISSN:
1551-2916
Source:
Blackwell Publishing Journal Backfiles 1879-2005
Topics:
Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
,
Physics
Notes:
Nanometric ammonium aluminum carbonate hydroxide (AACH) with a particle size less than 5 nm was produced from ammonium aluminum sulfate and ammonium hydrocarbonate under an optimized adding condition, and phase transformations of the AACH on heating and the effect of α-Al2O3 seeding on the transformation kinetics were investigated. The phase transformation sequence of AACH on heating was found to be AACH → amorphous Al2O3→γ-Al2O3→θ-Al2O3→α-Al2O3, where the formation temperatures of θ-Al2O3 and α-Al2O3 are 850° and 1050°C, respectively. The phase transformation sequence on heating of the AACH seeded with 5 wt%α-Al2O3 seed crystals 100 nm in diameter was found to be AACH → amorphous Al2O3→θ-Al2O3→α-Al2O3. γ-Al2O3 was not observed, and the θ-Al2O3→α-Al2O3 transformation temperature was reduced to 900°C by the seeding. By calcining the γ-AlOOH, the AACH, and the seeded AACH at their lowest temperatures to transform completely to α-Al2O3 (i.e., about 1200°, 1100°, and 900°C, respectively), α-Al2O3 powders have been obtained with mean particle sizes of about 150, 70, and 30 nm, respectively. The α-Al2O3 powder produced from the seeded AACH has the highest sintering reactivity. After sintering at 1400°C for 2 h, relative densities of the powder compacts of α-Al2O3 obtained by calcining γ-AlOOH, AACH, and the seeded AACH are 74.3%, 95.0%, and 98.5%, respectively.
Type of Medium:
Electronic Resource
URL:
http://dx.doi.org/10.1111/j.1151-2916.2003.tb03469.x
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